A related problem is persistence of both 4th arches.  After the intersegmentals come forward both the right and left 4th arches remain attached to the dorsal aorta.  This causes a vascular ring constriction of the esophagus and trachea in addition to the constriction caused by the ligamentum.

The surgical approach to this abnormality is to divide one of the aortic arches, whichever is least functional.  All 6 cases encountered in this hospital have had a small atretic left arch, in which case we divide the left arch and left ligamentum and leave the right arch as the functional arch, as illustrated in the following slides.